Electronically or digitally created signatures have been used more and more frequently in daily life. Currently, there are several ways to electronically capture a user's real signature. For example, the user can handwrite her signature on a piece of paper and then hold the paper in front of a camera such that the camera can take an image of the paper. Subsequently, the signature can be extracted from the image and saved in a digital form. As another example, the user can upload a scanned copy of a previously signed document to a computer, which then recognizes the signature on the scanned document and saves it in a digital form. For yet another example, the user can draw the signature by moving a mouse or trackball, or sliding a finger or pen on a touch-screen or trackpad.
These electronic signature capturing technologies makes it feasible to generate an electronic signature mimicking the user's real, handwritten signature, and thus have been widely used in various computerized transactions. For example, the user can electronically sign a document online, without the need of printing the document, physically signing it, and mailing the signed document to the recipient. Moreover, with the user's permission, the electronic signature can be reused for multiple documents, thereby saving the user the trouble of repeatedly signing multiple documents. As another example, a retailer can collect customers' electronic signatures at a point-of-sale (POS) terminal, and thus avoid the process of print paper receipts, requesting that the customers sign the receipts, and storing or archiving the signed receipts.
However, the existing methods for capturing an electronic signature are still burdensome because they require the presence of extra devices such as scanner, mouse, track ball, trackpad, touch-screen, etc., which may not be available in many settings. For example, it may not be feasible for a mobile POS machine or an automated teller machine (ATM) to carry a mouse or touch-screen. Moreover, the existing methods require people to write on a device (e.g., paper, touch-screen, trackpad) or manipulate a device (e.g., mouse, trackball) to create an electronic signature. This may be challenging to physically impaired people. For example, patients suffering from hand or finger arthritis often find it difficult, painful, or even impossible to use a mouse, touch-screen, or the like.